For years, the glitzy annual charity preview of the North American International Auto Show literally was the hottest ticket in town.

Even with as many as 17,500 tickets available, the black-tie affair would sell out, and auto industry insiders and others would scramble for the pricey tickets so they could see and be seen at one of Detroit’s highest profile parties of the year.

With tax-deductible tickets now costing $400 each, the event in many ways symbolizes the still considerable power and glamour of the auto industry in Michigan. On charity preview night, a long procession of limousines clogs the roads leading to and from Detroit’s Cobo Center, and thousands of elegantly dressed men and women crowd every upscale club, bar and restaurant in the city before and afterwards.

But even while local celebrities, television reporters and politicians hailed the preview as they do every year, proceeds and attendance were down significantly from previous years. The preview raised $6 million for 11 local children’s charities this year, down $800,000 from last year and about $1 million from 2005.

Some critics say Michigan’s struggling economy is not entirely to blame. Instead, they argue the event has been allowed to grow so crowded and “pedestrian” that many previous attendees have decided it’s no longer worth the hassle of dealing with the traffic, parking and excruciatingly long lines for bathrooms and coat check.

In comments reminiscent of a famous Yogi Berra quote, some who have crossed the charity preview off their “to do” lists say it’s so crowded, no one wants to go there anymore.

“It’s the last place I’d want to be on a Friday night,” says one auto industry insider, who insists he’s turned down free tickets.

“You can’t even see the cars,” because it’s so crowded, gripes another.

Another brewing problem: At least a few of Detroit’s largest auto suppliers, which traditionally have purchased big blocks of tickets to distribute to employees and customers – say show organizers now won’t give them the time of day.

The suppliers claim NAIAS officials repeatedly have snubbed them when they have asked to play a larger role in the auto show, media days and the charity preview.

“A lot of suppliers contribute a lot to the auto industry, and we’re not asked to be involved in the show,” one supplier vice president says. “It’s made very clear that suppliers are not welcome,” he adds, explaining there are lots of other black-tie charity events in metropolitan Detroit that welcome suppliers.

And, in fact, suppliers do play a much larger role in the rest of the world’s major international auto shows, such as Frankfurt, Tokyo and Paris.

Unique to the Detroit show, however, is an agreement barring competitors of supplier sponsors of NAIAS from participating. For instance, Michelin Group is the only tire maker allowed to exhibit at and sponsor the show, and Johnson Controls Inc. the only interior supplier.

At this year’s show, NAIAS officials were attempting to woo an electronics supplier to serve as a show sponsor and exhibitor.

Yet another problem slowing bulk ticket purchases: tough corporate ethics rules that don’t allow employees to accept tickets, even if they are for charity. “No one from GM, Ford or Chrysler will come unless they can reimburse us for the cost of the ticket, and that becomes too much of a hassle,” a supplier executive says.

But the troubles of Detroit’s auto industry most certainly are having an impact.

“More than 35 auto suppliers entered bankruptcy since 2000,” says a senior vice president at one major supplier. “The Street is expecting 10 more to file this year. We are all cutting everything that isn’t absolutely necessary to run and grow our businesses. This includes the charity preview.”

Robert Thibodeau Jr., senior co-chairman of NAIAS 2007, sees the glass as half full, pointing out the preview remains one of the largest charitable events of its kind in the U.S.

“We raised 6 million bucks in the face of a very tough economy,” Thibodeau says.

He says organizers noted declining waiting lists for the preview three years ago and declining ticket sales last year – as well as the troubles of some other major charitable organizations – and started working with the children’s charities, themselves, to find new ways to boost interest.

This effort has paid off, Thibodeau says. “We saw an influx of different (read non-automotive) people who were buying the tickets,” he says.

Acknowledging 2007 will be another challenging year, Thibodeau makes it clear organizers are open to suggestions and says they will be sitting down with the charities and, yes, even talking to auto suppliers, to brainstorm new ways to bolster ticket sales next year, whether it involves new types of entertainment or even a possible format change.

The 2007 charity preview already showed some improvements, even though it may have been sheer serendipity. Lower attendance decreased traffic problems around Cobo Center as well as bathroom lines. Plus, instead of the snow and cold that usually plague the evening, temperatures were freakishly warm, shortening coat-check lines.

While still crowded, it was easier to get close to many more of the vehicles than in previous years.

Chinese auto maker Changfeng’s exhibit in the basement was utterly deserted. But the aisles featuring the ultra-luxury brands were impenetrable masses of humanity crushed so tightly together you would have thought it was the deck of the Titanic and the Maseratis and Bentleys were the last lifeboats.

If organizers want to improve the charity preview, that should be ground zero.